In general, a test board or a burn-in board is provided with a socket device for testing a semiconductor device (IC). Input and output leads of the board (a test board, a burn-in board) are connected to the burn-in chamber or a peripheral device thereof or an extra test device so that power and electrical signals may be input or output for operating the IC and for measuring characteristics of the IC. That is, the socket device for a semiconductor device is used in a system for a series of IC tests.
Among widely used general ICs, a BGA type IC remarkably reduces the size and thickness of the IC by arranging leads of the IC, or balls on the whole surface of the IC.
Recently, the pitch between balls of the BGA type IC has decreased from 0.5 mm to 0.4 mm to 0.35 mm, etc., and the number of used balls has increased to two hundred to five hundred to several thousands.
An LGA type IC is an IC without having balls on a pad (or a land) in the BGA type IC.
In recent years, the LGA type IC and the BGA/LGA hybrid IC have been available in a variety of forms, and a socket for testing the LGA type IC or the hybrid type IC is provided with a plurality of contacts having predetermined vertical elasticity, and the lower leads of the contacts are connected to a printed circuit board (PCB) by contacting or soldering.
Here, the upper leads of the contacts are provided such that the upper leads of the contacts contact the leads of the semiconductor device loaded in a socket, and for achieving electrically safe contact, the socket is provided with a pressing device for pressing down the IC.
For reference, when an external force applied by the pressing device on the upper surface of the semiconductor device is divided by the number of contacts, a physical force applied to one contact is calculated.
More specifically, a physical force applied to one contact is roughly 20 gf. For example, when the number of leads in the IC is two hundred, it is estimated that a physical force of about 4.0 kgf is required to be applied to the semiconductor device.
Accordingly, a socket for testing the IC is provided with a latch capable of effectively applying a powerful external force as described above to the IC. The socket for testing the semiconductor device is provided with extra power and reliable contacts enabling stable signal transfer.
FIGS. 1(a), (b), and (c) are a plan view, a side sectional view, and a bottom view of a BGA/LGA hybrid IC, respectively.
Referring to FIGS. 1(a), (b), and (c), an upper surface of the semiconductor device 1 is provided with fine protrusions 2 similar to the surface of sandpaper. The central part of a lower surface of the semiconductor device is provided with a plurality of balls 3 as leads of the semiconductor device. Land (or pad) type leads 4 are arrayed on an area outside of the plurality of balls 3, which result in manufacturing the BGA/LGA hybrid IC.
Currently, such hybrid-lead type ICs are being developed and are produced in various forms. Thus, a variety of socket devices is necessary for testing such ICs.
Particularly, in case of the BGA/LGA hybrid IC, a BGA part and an LGA part may be sometimes tested separately, but urgently needed is the development of a socket device that enables simultaneous testing of the BGA part and the LGA part.
The total number of leads in the BGA/LGA hybrid IC is about two hundred. It is necessary that the contacts for testing the LGA part, which run upward from below the semiconductor device, come in contact with leads (a pad or a land) beneath the semiconductor device. Furthermore, in this case, it is necessary that the socket device be provided with a device for pressing down the semiconductor device, wherein the pressing-down force should be equal to or higher than a total force all the contacts may sustain.
FIGS. 2(a) and (b) are a top plan view of a socket device for testing the semiconductor device according to a related art and a sectional view taken along line A-A of FIG. 2(a), respectively.
Referring to FIGS. 2(a) and (b), the related art socket device 10 for testing an LGA type IC includes a socket body 11 provided with a plurality of curved contacts 12, a socket cover 13 moving vertically above the socket body 11, and a latch 14 combined with the socket body 11 that can rotate so as to hold or release the LGA type IC 20 while operating in cooperation with vertical movements of the socket cover 13.
The latch 14 is provided with a guide slot 14a, and a guide pin 15a is engaged with the guide slot 14a. The guide pin 15a is coupled to a driving link 15, one end of which is hinged on the socket cover 13. The latch 14 is elastically biased by a coil spring 16.
When the socket cover 13 is pressed in the related art socket device, the latch 14 opens outward and the semiconductor device may be loaded. When the socket cover 13 is free from the pressing, due to a restoring force of the coil spring 16, the latch 14 presses down and holds the upper surface of the semiconductor device.
In the related art socket device, the front end of the latch presses and holds the upper surface of the semiconductor device by applying strong force. This step is performed repeatedly with each new test. As the upper surface of the semiconductor device is rough, when the front end of the latch is used repeatedly over a period of time, the front end of the latch in contact with the semiconductor device wears out more and more as the number of the tests increases. As a result, the electrical contact between the leads of the semiconductor device and the contacts becomes unstable, and thus reliability of the test decreases.
When tested about fifty thousand times, the front end of the latch wears out and thus malfunctions.
In the related art socket device for testing the LGA type IC, it is required to arrange and assemble contacts with the additional parts required in putting together the contacts having a bow-type curved section. The number of the parts is great, so assembly thereof is difficult. The related art socket device is also required to be provided with a structure for pressing to hold the semiconductor device with a strong force, and with a driving device, which results in a complex structure of the socket device. Particularly, due to the complex structure of the socket device, the price of the socket device increases and overall quality of the socket device decreases.